International Research Journal of Engineering and Technology (IRJET)
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STATCOM based Control Scheme for Power Quality Improvement in GridConnected wind Energy System with Non-Linear Load
K. Jaya Shankar1, Dr. G. V. Siva Krishna Rao2
1PG
scholar, Dept. of Electrical Engineering, Andhra University College of Engineering, Visakhapatnam, A P, India.
Dept. of Electrical Engineering, Andhra University College of Engineering, Visakhapatnam, A P, India.
----------------------------------------------------------------------***------------------------------------------------------------------------2Professor,
Abstract: Generally, the non-conventional energy sources
are being extensively used in case of power electronic
converter based distribution systems. This paper mainly
focuses on the wind energy system integrating with grid
connected system and also improvement of power quality
features. The wind energy power plant is modelled based
on associated equations. For improving this power quality
problems, this paper proposes the concepts of shunt
converter controllers. This paper also proposes the
concepts of PQ-theory based Static Compensator. And also
the results are compared for this cases. Thus with such a
control, a balanced load currents are obtained even in the
presence of non-linear load. The experimental setup is
done in Matlab and verified the simulation results.
The power flow controlling device is a device
which is used for varying and controlling the system
parameters [3].
A shunt device is a compensating device i.e. which
is connected between the grid connected point called as
PCC and the ground [4]. Shunt device either can absorb or
generate the reactive power for controlling the magnitude
of voltage at point of common coupling. The reactive
power compensation is also one of the applications of
shunt converter devices [5].
Figure 1 shows the basic diagram for the shunt
connected inverter based grid connected system[6].
Index Terms—SVC, distributed generated system (DG),
distribution system, and renewable energy.
1 .INTRODUCTION
Generally, with increase in the power demand due
to increase in population, utilization, the Generation of
power was really a challenge now a day. Due to high
utilization of non-conventional energy sources [1] as a one
of the distribution energy source, may causes the stability
problems such as voltage regulation and other power
quality problems. Therefore, the power electronic based
forced commutated converters are preferred in
distribution system for maintaining the system stability,
reliable performance and efficient work and also
improving the quality of power at coupling junction point.
The current distortions in non-linear load may
result same distortions in the system voltages and in some
cases also shows the serious effect on power system.
Generally, the problems in power system are more
complicated and also have difficult to identify the problem
when we integrate the wind energy system with grid
connection [2]. If this problems continuous, it’s mainly
causes the damage of system and also reduces the system
efficiency. By controlling the system parameters such as
magnitude of voltage, transmission impedance and load
angle then we maintain the power flow.
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Fig 1: Diagram for Proposed System.
2. Grid Interconnection of Wind Energy System
Recently grid connected wind system have been
spreading in residential areas and in industrial areas. So
we have to find a suitable MPPT technique that gives a
better power output when connected is to find out. For a
grid connected system there are certain factors that have
been considered such that DC-AC conversion with highest
output power quality with the proper design of filters
System main controlling factors like MPPT. Grid interface
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International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 06 Issue: 09 | Sep 2019
p-ISSN: 2395-0072
www.irjet.net
inverters which transfers the energy from the wind energy
generation system to the grid by maintaining constant of
dc link voltage. For a grid connected system the utility
network mainly demands for better power quality and
power output. In the case of voltage fluctuations control of
grid parameters is very difficult. So for a wind system that
is connected to a grid first stage is the boosting stage and
the second stage is DC-AC converter [7]. An output filter is
usually employed which reduces the ripple components
due to switching problems. The problem associated with
the grid connected system is that the dc link voltage that
must be oscillates between the two levels which depends
on the operating climatic conditions (ambient temperature
& irradiance) in which inverter which acts us a power
controller between the dc link and the utility. Dc link is
generally used to isolate between the grid side and the
inverter side so that we can control both wind system and
grid separately. All the available power that can be
extracted from the wind system is transferred through the
grid [8]-[9].
2.1 Wind Energy System:
The generation of electrical power is obtained
mainly in two ways i.e one is conventional source and
other is non- conventional energy sources. The generation
of electricity using non-renewable resources such as coal,
natural gas, oil and so on, shows great impact on the
environment by production of pollution from their general
gases. Hence, by considering all these conditions the
generation of electricity is obtained from the renewable
energy sources.
Fig.2 basic schematic diagram of wind turbine
And the coefficient of power also plays a key role
for wind system and the basic minimum value of power
coefficient is 0.5. The power coefficient is obtained by the
ratio of tip speed ratio to pitch angle. The pitch angle is the
angle to which the blades of turbine is arranged based on
their longitude axis and changing of wind direction. The tip
speed ration is defined as ratio of linear speed of the rotor
to the wind speed.
Fig.3 shows a typical waveform for coefficient of
power with respect to the tip speed ratio. The maximum
achievable range of TSR is from 0.4 to 0.5 for turbine with
high speed and from 0.2 t0 0.4 for turbine with low speed
[14].
Basically, out of all renewable energy sources the
wind turbine plays an important role for generating
electricity. And also from economical point of view the
wind turbine has low maintainece cost because it needs no
fuel so that it is pollution free. Mostly, in present world 5060 percent [13] of energy is generated from wind turbine
as compared with all other renewable energy sources.
The wind turbine converters wind energy to
electrical energy and the generator mechanical shaft
power is obtained by the following expression:
Fig 3: Power coefficient Vs Tip Speed Ratio
3. STATCOM and Its Control Technique:
The typical layout of wind power generation as
shown below.
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A STATCOM is built with Thyristors with turn-off
capability like GTO or today IGCT or with more and more
IGBTs.A STATCOM based control technology has been
proposed for improving the power quality which can
technically manages the power level associates with the
commercial photo voltaic system. The proposed Solar
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Volume: 06 Issue: 09 | Sep 2019
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based STATCOM control scheme for grid connected photo
voltaic energy generation for power quality improvement
has following objectives.
• Unity power factor at the source side.
•Reactive power support only from STATCOM
Generator and Load.
to wind
• The Dc voltage is obtained for STATCOM is generated
from Solar Cells.
damping enhancement. The PID controller is designed
using the Model Control Theory. The mathematical
modelling of the controller is given in [10]. The control
scheme used here is shown in the Figure 5.
Vsm={2/3(V2sa+V2sb+V2sc)1/2}………………(a)
The in-phase unit vectors are obtained from AC
source phase voltage and the RMS value of unit vector Usa,
Usb, Usc as shown in (b)
A STATCOM is a controlled reactive-power source.
The STATCOM is connected to the power system at a PCC
(point of common coupling), through a step-up coupling
transformer, where the voltage-quality problem is a
concern [10]. It provides voltage support by generating or
absorbing reactive power at the point of common coupling
without the need of large external reactors or capacitor
banks. Using the controller, the VSC and the coupling
transformer, the STATCOM operation is illustrated in
Figure 4.
……….(b)
From
source
Unit vector
Usa, Usb, Usc
STATCO
M
CONTRO
LLER
Power flow
Generation
Transmission Line U T
Load
PCC
Vdcref
Coupling X T
Transformer
Iq
Reactive current
injection
limiter
iSabc
4. SIMULATION STUDY:
Phase
UT
U
Controller
DC voltage
GATE
PULSE
Figure 5: Control Diagram
3-phase AC voltage
Voltage
source
converter
X
The proposed control scheme is simulated using
SIMULINK in power system block set. The main block
diagram of the system operational scheme is shown in
Figure. 1. The simulation diagram of the proposed PV cell
based grid interfaced system using Statcom is as shown in
figure 6.
Uref
Firing angle
Vdc
Cdc
Figure 4: Basic Block Diagram for Static Compensator
The utilization of different types of electrical loads
in three phase system, produces an unbalances in current,
which causes the unreliable power. Thereby for
maintaining the electrical reliability the statcom controller
plays a key role. In this statcom control technique, the
reference voltage and dc link capacitor voltages are
compared and the result obtained from this is converted to
two phase coordinators called as orthogonal vectors.
The STATCOM acts either as a source or a sink of
reactive power. It provides voltage support by injecting or
by absorbing reactive power at the point of common
coupling without any large external reactors or capacitor
banks. Here we use a PID controller with STATCOM for
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Volume: 06 Issue: 09 | Sep 2019
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Figure 8: FFT analysis for Source current.
CONCLUSION
Figure 6: Simulation Diagram of Proposed Grid Connected
System
In figure 7 the wave form (a) shows the output for
source current after compensation, (b) waveform for load
current, (c) waveform for the injected current by the
Statcom converter and finally the waveform (d) shows the
result for current from wind turbine. Figure 8 shows the
total harmonic distortion of proposed system with Statcom
controller
The paper presents the STATCOM based control
scheme for power quality improvement in grid connected
wind energy system linked with non-linear load. The
power quality issues and its consequences on the
consumer and electric utility are presented. The operation
of the control system developed for the STATCOM-PV in
MATLAB/SIMULINK for maintaining the power quality is
simulated. It has a capability to cancel out the harmonic
parts of the load current. It maintains the source voltage
and current in-phase and support the reactive power
demand for the solar panel and load at PCC in the grid
system, thus it gives an opportunity to enhance the
utilization factor of transmission line. The integrated grid
and STATCOM with PV have shown the outstanding
performance.
REFERENCE
[1] Qing-Chang Zhong, Senior Member, Cascaded Current–
Voltage Control to Improve the Power Quality for a GridConnected Inverter With a Local Load” in IEEE
TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 60,
NO. 4, APRIL 2013.
[2] K. S. Hook, Y. Liu, and S. Atcitty, “Mitigation of the wind
generation integration related power quality issues by
energy storage,” EPQU J., vol. XII, no. 2, 2006.
[3] R. Billinton and Y. Gao, “Energy conversion system
models for adequacy assessment of generating systems
incorporating wind energy,” IEEE Trans. on E. Conv., vol.
23, no. 1, pp. 163–169, 2008, Multistate.
Figure 7: simulation result for current.
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[4] Wind Turbine Generating System—Part
International standard-IEC 61400-21, 2001.
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International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 06 Issue: 09 | Sep 2019
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[5] J. Manel, “Power electronic system for grid integration
of renewable energy source: A survey,” IEEE Trans. Ind.
Electron., vol. 53, no. 4, pp. 1002–1014, 2006, Carrasco.
[6] M. Tsili and S. Papathanassiou, “A review of grid code
technology requirements for wind turbine,” Proc. IET
Renew.power gen., vol. 3, pp. 308–332, 2009.
[7] S. Heier, Grid Integration of Wind Energy Conversions.
Hoboken, NJ: Wiley, 2007, pp. 256–259.
[8] J. J. Gutierrez, J. Ruiz, L. Leturiondo, and A. Lazkano,
“Flicker measurement system for wind turbine
certification,” IEEE Trans. Instrum. Meas., vol. 58, no. 2, pp.
375–382, Feb. 2009.
[9] Indian Wind Grid Code Draft report on, Jul. 2009, pp.
15–18, C-NET.
[10] C. Han, A. Q. Huang, M. Baran, S. Bhattacharya, and W.
Litzen berger, “STATCOM impact study on the integration
of a large wind farm into a weak loop power system,” IEEE
Trans. Energy Conv., vol. 23, no. 1, pp. 226–232, Mar. 2008.
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